Coating oven with catalytic incineration of volatiles



R. J. RU FF Ngv. 9, 1965 COATING OVEN WITH CATALYTIC INCINERATION OF VOLATILES Filed Feb. 9. 1962 Z5 Sheets-Sheet 1 /N VEN TOR# Richard J. Ruff 5y' 5M?, A TTORIVEYS.v

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COATING OVEN WITH GATALYTIC INCINERATION OF VOLATILES Filed Feb. 9, 1962 s sheets-sheet 2 TTOR EYS R. J. RUFF Nov. 9, 1965 COATING OVEN WITH CATALYTIC INCINERATION OF VOLATILES 3 Sheets-Sheet 5 Filed Feb. 9, 1962 Bte@ E SE m. minut mm. .Cummml .m Sagl N V EN TOAl Ric/70rd J. Ruff m45; y w

A 7' TH/VEYS United States Patent OE 3 ,2 l. 6,12 7 Patented Nov. 9, 1965 lice 3,216,127 COATENG OVEN WITH CATALYTIC INCNERATHON F VLATILES Richard J. Ruff, Detroit, Mich., assigner to Universal Oil Products Company, Des Plaines, lli., a corporation of Delaware Filed Feb. 9, 1962, Ser. No. 172,241 3 Claims. (Cl. 34-54) This invention relates to improved -apparatus for effecting the heat treating of coated articles and more specifically to an improved coating oven construction which has means for catalytically incinerating the Volatile components entrained in the treating air stream.

The treating apparatus of this invention may he utilized to heat treat many different types of coatings on many different articles and materials, but is primarily designed to heat treat protective coatings or printing applied to sheet metal materials. It should be understood that the drawing and the descriptive material is for illustrative purposes and that the apparatus may be used for other heat treating purposes.

In the manufacture of containers, such as beer cans, coffee cans, containers for fruit juices, etc., decorations are coated and printed on sheet metal plates prior to their being formed into a container. In some instances it is necessary to supply a background coating which is baked onto the sheet metal prior to application of the decorative coating, some or which may be in varying colors. Also in connection with certain types of containers such as beer cans and food containers, there is a protective lacquer coating applied to the inside of the container and this is normally applied to the sheet metal material prior to formation of the container.

Generally heat treating ovens operate at speeds accommodating more than 100 sheets per minute such that the amount of solvent evaporated in the treating and drying process may be as much as 150 gallons per hour, or more. Thus, there is produced a considerable quantity of -fumes during the operations of these types of drying ovens which are odorous and obnoxious in character, as well as arnmable. In the usual heat treating or coating oven installation, there is a resulting high requirement of fresh air introduction into the oven for diluting the v-aporized solvents to a sufficient extent to prevent any danger of tire and at the same time prevent condensation of vaporized solvents which would result in creating a fire hazard and require frequent cleaning of the oven and associated equipment. Also, in connection with prior installations, large quantities of air are required to be passed through coating ovens so that there is oven exhaust ventilation and dilution provided primarily to meet established safety standards, with little or no regard for air pollution that may result. On the other hand, the present improved apparatus provides catalytic incinerating means for insuring a substantially complete oxidation and elimination of obnoxious volatile components such that there is a resulting non-flammable and non-objectionable exhaust stream from the oven. In permitting unoxidized or non-catalytically treated volatiles to escape from a heating treating oven, as by the use of excessive amounts of Ventilating and diluting air, there is a definite reduction in the efficiency of the oven, for when operating at reduced material and solvent loadings, the excess `fresh air supply results in materially increasing the heat input requirements to the unit and thereby a materially increased cost of operation. Attempts have been made to overcome this ineiiiciency by utilizing an explosimeter in the unit which operates to vary the supply of fresh air in accordance with the solvent loading to the oven, and such systems have been utilized with the tacit approval of insurance underwriters; however, it is believed that the practice is somewhat dangerous in that there is an appreciable lag in the operation of the system and it is entirely possible that a sudden full solvent load into the oven will not have a sufficient supply of fresh air to maintain conditions in which no fire hazard is present.

The use of catalytic incineration, as provided in combination with the present heat treating oven design and construction, provides means for rapidly reducing, by oxidation, the solvent loading in the vent gas stream to eliminate odor and fire hazard. It should be pointed out also that insurance underwriter requirements for reducing the fire hazard by diluting volatiles in the air stream to one-fourth of the Lower Explosive Limit (LEL) 4of the particular type of vapor is a waste of potential energy. For example, an oven vented to provide the 25% LEL carries away energy that is capable of raising its own temperature approximately 660 F., based upon the fact that the B.t.u. release in a cubic foot of dry air (at standard F. density) will raise its temperature ap-` proximately 55 F. and that there are 12 B. t.u.s per standard cubic foot in the diluted air stream. It is thus of definite advantage to provide, in accordance with the present construction, a drying oven or heat treating apparatus which will oxilize through catalytic action the volatiles in the fume laden air and make available the heat from such oxidation to heat the air stream being introduced into the drying zone or zones. The heat available from such oxidation will normally be adequate to supply the total heat requirements of the oven, with auxiliary heat being used primarily for startup purposes.

In the design of drying ovens for -certain usages, it is desirable to provide a construction wherein the solvent release is substantially confined to the initial heating zone. Also, in some heat treating operations, it is of advantage to have a once through fiow of the drying air stream in order to avoid return of contaminated gas to the oven in the event of any equipment malfunctioning, or to preclude the entry of anything to the oven other than a heated fresh air stream.

It is therefore a principal object of the present invention to provide an improved modified form of heat treating oven which catalytically incinerates all of the combustible components being discharged from the treating chamber.

A further object of the invention is to provide a modified construction and arrangement effecting the automatic -control of the fresh air stream to the coating oven and a channeling of all of the fresh air intake flow to the initial treating zone of the unit, whereby to etfect the venting of the vapor and fumecontaining gas stream through a catalytic incineration zone operating in conjunction with only the initial heat treating zone of the unit.

A still further object of the invention is to provide a heat exchange arrangement that passes the bulk of the fresh air treating stream in indirect heat exchange relationship with the hot incinerated exhaust stream such that there is a heat recuperative operation to effect improved efiiciency and a lowering of heat requirements of the overal1 operation.

In a broad aspect, the present invention provides an improved coating oven for heat treating coated articles t0 evaporate and dry coatings `and remove combustibles from the vaporized solvents, said oven comprising in combination, an elongated heat treating chamber, means for conveying articles to be heat treated through the chamber from an entrance end to an exit end, a first heating section in the chamber adjacent the article entrance end thereof, at least one additional heat treating section in the chamber, a plenum section within said first heat treating section arranged to direct heated gases over the articles passing therethrough, a vapor exhaust duct from said first section, a circulating fan connecting with said exhaust duct, a vapor combustion section connecting to and extending downstream of said circulating fan, heat supplying means within said combustion section, catalytic vapor incinerator means disposed across said combustion section downstream of said heat supplying means, a heat exchange section connecting with said combustion section and having passageway means therein to receive and dischargefoxidized exhaust gases from said combustion section, additional passage-way means in said heat exchange section extending adjacent to and in heat exchange relationship with first said passageway means that have fresh air inlet means thereto and heated air outlet means therefrom, whereby to pass air in indirect heat exchange relationship with oxidized exhaust gases from said combustion section, a heated air duct extending from said heated air outlet means and said plenum section in said first heat treating section, regulat'able damper control means across at least a portion of the heated air duct from said heat exchange section, a recirculating fan in said heated air duct, adjustable air inlet means to said heated air duct upstream of the recirculating fan therein for introducing tempering air thereto, an exhaust gas outlet stack connecting to and extending from the downstream end of said exhaust gas passageway means of said heat exchange section, and means for recirculating drying gases through the additional heat treating of the chamber to continue the drying of the coated articles passing therethrough.y

A preferred construction and arrangement interconnects the damper control means regulating the flow of heated fresh air to the oven with damper control means regulating tempering air into the heated air duct and, in turn, automatically regulates and controls the interconnected dampers by means of a t-hrottling controller which operates responsive to temperature sensitive means in the flow path of the heated air stream entering the oven. In other words, where it is desired to reduce the temperature of the air stream, the control means will serve to adjust the dampers in the heated air stream flow path to reduce the volume of air therethrough, while at the same time opening the `dampers introducing tempering air into the hot air duct such that there is an overall temperature reduction in the confined stream passing to the heat treating oven. In the reverse situation, where additional heat is required, the dampers in the hot air duct are opened up and the tempering air dampers are closed down to controllably diminish or preclude dilution of the hot air stream.

In the usual heat treating oven construction there are a plurality of heating zones, with hot air being recirculated around the coated sheets or articles to -be treated in order to insure complete treating and drying of all coatings prior to the discharge of the articles from the oven zone. It is, however, a feature of the present improved construction and arrangement to permit fresh air introduction into the oven at only the inlet and outlet ends of the conveyor system, together with the heated fresh air stream that is recuperatively heated in the catalytic oxidation-heat exchange zone and then introduced into the initial drying and solvent removal zone of the oven unit. Thus, additional heat treating zones which are positioned downstream from the initial solvent removal zone, with respect to conveyor movement, utilize merely a recirculation of the air stream in the oven, with additional heat being added by means of iburners or other heating means associated with the recirculation flow path. Air pressures are balanced throughout the lengt-h of the oven unit by the operations of the various air circulating fans, including those feeding the initial heat treating zone and the catalytic combustion zone, together with such other recirculating fans as may be desired for use in connection with subsequent heating zones, such that the fresh air taken into the oven unit at the conveyor discharge end may -be contin- CII uously moved forwardly to the initial heat treating zone to become mixed with the fresh air introduced thereto. As a result, all of the fresh inlet air to the oven unit is necessarily passed through the catalytic combustion zone and is discharged from a single exhaust stack, after heat exchange passage with the bulk of the fresh air inlet stream to the oven.

Reference to the accompanying drawings and the following description thereof Iwill serve to show further advantages and novel construction features in connection with the modified catalytic oxidation system in accordance with the present invention effecting the elimination of noxious flammable fumes from the heat treating oven.

FIGURE l of the drawings is a diagrammatic elevational view of a coating oven having :a catalytic fume incinerating section in combination therewith.

FIGURE 2 of the drawings is a partial plan view of the coating oven, as indicated by the line 2 2 in FIG- URE 1.

FIGURE 3 of the drawings is a diagrammatic -sectionalelevational view, as indicated by the line 3 3 in FIG- URE 1.

FIGURE 4 of the drawings is a combination sectional and end view of the initial treating section of the coating oven, as indicated by the line 4 4 in FIGURE 1.

FIGURE 5 of the drawings is a sectional view showing diagramnratically a hot gas recirculating section in connection with the oven unit, as shown by the line 5 5 in FIGURE 1.

FIGURE 6 of the drawings is a partial elevational view of the damper control section as indicated by line 6 6 in FIGURE 2 of the drawings, together with a diagrammatic indication of automatic control means for operating the adjustable dampers associated with the heated air duct.

Referring now to the drawings there is shown an elongated coating oven chamber 1 having a top cover section 2 and side walls 3 and 4 which are supported on a suitable oor or foundation 5. It will be noted that the upper and side wall portions are indicated diagrammatically as having a suitable insulation to preclude heat loss from the unit, however, it is not intended to limit the present invention to any one type of insulation or to means for attaching the insulation to the walls of the heat treating oven, or to the fume combustion and heat exchange sections.

An endless conveyor 6 having wickets 7, or other suitable means attached thereto, for receiving and supporting the sheets or articles to be treated, are mounted within the interior of the oven chamber 1 on suitable trackways 8 and 9. Suitable means, not shown, are provided for introducing or inserting the metal sheets into the wickets 7 at the inlet end of the conveyor system and for subsequently removing the dried and coated metal sheets from the discharge end of the oven unit.

Thus, the wickets carry the sheet metal pieces, or other articles, through the longitudinal upper section of the oven chamber and return empty along the lower half portion of the unit. Generally the oven unit will have an initial or first heat treating zone 10 and one or more additional heat treating zones 11 which are downstream, with respect to conveyor movement, from the inlet end of the oven chamber 1. The latter will be open only at the two ends thereof such that infiltrated air can only enter from the inlet and discharge ends of the oven, where the conveyor system necessarily emerges therefrom. All additional fresh air intake to the drying system is provided from a heated fresh air system that is in combination with the combustion and heat exchange sections superimposed above the initial heat treating zone 10.

An enclosed chamber 12, having a top wall section 13 and side wall sections 14 and 15, is, as indicated, superimposed above the inlet end of the chamber 1 to effect the desired catalytic combustion of obnoxious volatile components in the discharge gas stream as well as effect the recuperation of heat therefrom. Heated air is actually distributed to the interior of the initial heat treating zone through a plenum chamber 16 which is positioned longitudinally between the upper and lower sections of the conveyor belt system 6. The chamber 16 has upper louvers or perforations 17 suitable for discharging heated air through the plurality of wickets and spaced sheet metal pieces to effect the desired drying thereof and the volatilization and entrainment of flammable vapors. The hot air stream with entrained vapors is collected in an upper longitudinal manifold or gas collection section 18 which has the lower face thereof provided with suitable louvers or perforations 19 for admitting the vapor containing stream.

A suitable opening or passageway 20 is provided from the top of the chamber 1 into the lower portion of the upper chamber 12 so as to provide for the flow of the solvent containing air stream into the interior of the combustion section. In the present embodiment, a pair of dampers 21 are shown transversely across the duct or passageway 20 to provide means for adjusting the air flow through said zone where it may be desired to balance ows within the unit. As best shown in FIGURE 3 of the drawings, manually operated positioning means 22 connect with the damper means 21 for adjusting the position of such damp-ers in the duct 20. Within the lower portion of the upper chamber 12 is a transverse partitioning member 23 which serves to define a lower gas passageway 24 that extends to the end portion of chamber 12 and feeds into an interiorly positioned fan or blower 25. The latter serves to insure the withdrawal ofthe fume laden air stream from the collection duct 18 in the heat treating chamber 10 and the discharge of such stream to a combustion section 26 maintained downstream within the chamber 12. The actual outlet of fan chamber 25, within the combustion section 26, is at the zone of suitable heat supply means such as burners 27 to which a fuel and air are supplied by means of line 2S extending through wall14 of the chamber 12.

Fumes in the exhaust gas stream pass from the burner zone uniformly through catalyst units 29 which extend transversely across the combustion section 26 to effectively carry out the catalytic oxidation of all entrained burnable fumes in the discharge gas stream. The catalytic incinerating means 29 may be of the type disclosed in the patent to Suter et al No'. 2,658,242, dated November 10, 1953, and covering metal wire or ribbon coated with amorphous platinum and/or palladium, or other noble metals such as osmium, ruthenium, rhodium. Catalytic units are generally formed from flat mats of coated crimped alloy metal ribbon, or from coated metal alloy screens, or from a combination of screens and ribbon cores. The platinum or palladium coating is usually electrodeposited on the ribbon an-d screens after suitable cleaning and preparation steps insuring a good bond of the plated coating. The finished elements are of such nature that upon heating the same to ignition temperature and supplying suitable mixtures of fuel and air thereto, catalytic oxidation will take place on the surface thereof resulting in the liberation of radiant heat energy. It is understood that any other suitable type of catalytic oxidation element may be employed in the incinerator means. Further detailed description of this incinerating means, however, is believed unnecessary herein, reference being made to the foregoing patent for this purpose.

A substantially horizontal transverse partitioning member 30 extends between side member 14 and 15 to separate the combustion section 26 from the heat exchange section 31 superimposed in the upper portion of chamber 12. The plate member 30 stops short of the one end of charnber 12 in order to provide for a passageway 32 which receives resulting combustion products passing downstream from catalyst units 29 and to in turn permit their distribution through a plurality of heat exchange tubes 33. The latter extend longitudinally in a heat exchanger bank through and between end tube sheets 34 and 35. Thus, the exhaust gases may be passed from the gas passageway 32 through the plurality of tubes 33 to a downstream gas collecting section 36 which in turn communicates through opening 37 to a stack 38. Generally, after catalytic combustion has been initiated in the catalyst elements 29, the heat supplied from burners 27 will no longer be necessary, and the heat from the catalytic combustion will sustain the high temperature operation in the initial heat treating zone 10 ofthe oven 1.

In order to recuperate heat from the combustion zone of the apparatus, a fresh air intake 39 is provided in the side wall 14 of the chamber 12 permitting air to pass in indirect heat exchange relationship with the hot gas tubes 33 and effect simultaneously the heating of the intake air stream and the cooling of the exhaust gas stream. As is best shown in FIGURES 3 and 4 of the drawings, a heated air discharge opening 40 is provided in the side wall 1S to connect with a heated air outlet duct 41 which in turn communicates with, and discharges into, a mixing chamber 42 through a set of adjustable dampers 43. The hot air stream then passes through a fan chamber 44 and a transfer duct 45 to the plenum chamber 16, which in turn effect the longitudinal spreading of the heated air stream and its upward distribution through louvers or perforation 17 to lche wickets 7 carrying the coated sheets which are to be dried or heat treated.

In order to provide automatic control of the air temperature, a suitable tempering air inlet opening 46 is provided on the side of the mixing chamber 42 and a set of adjustable dampers 47 are provided therein to control air flow into the interior of the chamber. A recirculating fan or blower 44 is housed within the chamber or duct work 44 and maintains circulation of the air stream to the plenum section. In FIGURE 6 of the drawings, there is shown diagrammatically an interconnecting linkage between the hot air dampers 43 and the tempering air dampers 47 whereby an automatically operating and throttling control means will effect the adjustment of the damper settings responsive to a temperature sensitive means 48 in the path of the hot air being introduced into the plenum chamber 16 of the `heat treating oven. Specifically, there is indicated diagrammatically suitable linkage means 49 connecting with dampers 43 and additional linkage means 50 connecting with dampers 47, both being connected to a movable arm 51 that in turn is connected to a power operated regulator 52. The latter may be either electrically or pneumatically operated to effect the desired movement of the linkage means 49 and 50 to in turn effect the adjustment of the dampers. The temperature sensitive element 48 connects through line 53 to a throttling controller 54 that in turn actuates the regulator 52. Air supply lines 55 and 56 indicate means for pneumatically controlling regulator 52 responsive to the controller 54 and the temperature indicator 48.

The linkage means 49 and 50 is, of course, merely diagrammatic and may encompass gearing or other suitable mechanisms for connecting to and turning the respective sets of dampers 43 and 47. In other words, it is not intended to limit the present invention to the use of any one type of linkage means or to any one type of power operating, regulator or controller for carrying out the adjustment of the dampers. It is, however, a feature of the present invention to provide interconnecting linkage between the dampers in order that one set opens in an opposing manner to the other. In other words, when dampers 43 are operated to reduce the quantity of hot air going to the heat treating oven, then the dampers 47 are adjusted to open slightly and introduce a regulated quantity of cooling or tempering air through opening 46. Conversely when dampers 43 are opened to a maximum extent, then dampers 47 will be maintained substantially closed to preclude the intake of any cooling air into the hot air stream.

As previously set forth above, in providing a long drying oven having an elongated continuous conveyor system, one or more additional heating zones 11 may be incorporated throughout the length of the oven chamber 1. In FIGURES l and 5, there are indicated diagrammatically means for reheating and recirculating a portion of the hot air stream being maintained throughout the 1ongitudinal length of the oven. Hot air is circulated from fan 57 into duct 58 and plenum chamber 59, which in turn has upper louvers or openings 60 to distribute hot air transversely across the multiplicity of wickets and retained coated sheets. The used and cooled air stream is collected in a manifold duct 61 which extends longitudinally along an upper portion of the chamber 1 and in turn channels the air stream through a passageway 62 into a transverse passageway 63 in a superimposed heating chamber 64. The end of the chamber is provided with a heat supply burner 65 which adds supplemental heat to the recirculating air stream within chamber 64 permitting reheated air to be discharged through an opening 67 into the fan chamber 57 and thence to the recirculation duct 58. A suitable vertically positioned partitioning member 66 extends longitudinally within the superimposed chamber 64 to provide the passageway 63, which in turn channels the recirculated air stream to the burner end of the chamber 64 whereby hot combustion gases may intermingle with the air stream recirculated to the plenum section 59. Where combustion gases are deemed undesirable to add to the hot air recirculating zones, then electrical heater or indirect heating means may be provided in lieu of burners 65 for adding heat to the air stream being recirculated to the one or more plenum sections 59.

It will be obvious that various changes or modifications may be made in the design or configuration of the passageways or treating zones within the scope of the present invention without departing from the scope or spirit thereof. Also, it may be noted that the conveyor 6 and wickets 7 will absorb a signicant portion of the heat input to the heat oven and the lower flight of the conveyor in the present embodiment passes through a relatively cool zone, so that, if desired, in a modified embodiment, it may be found advantageous to channel a portion of the hot air stream passing to the initial heating zone, or a recirculated air stream, to a preheating section which will serve to preheat the wickets prior to their entry into the upper heat treating section 10 at the inlet end of the oven chamber 1.

I claim as my invention:

1. A coating oven for heat treating articles to evaporate coating solvents and remove combustibles from the vaporized solvents, said oven comprising in combination:

(a) an elongated heat treating chamber,

(b) means for conveying articles to be heat treated through said chamber from an entrance end to an exit end,

(c) a first heat treating section in said chamber adjacent the article entrance end thereof,

(d) at least one additional heat treating section in said chamber,

(e) a plenum section in said irst heat treating section for directing heated gases over the articles passing therethrough,

(f) a vapor exhaust duct from said rst heating section,

(g) a circulating fan in said exhaust duct,

(h) a vapor combustion section connection to and extending downstream of said circulating fan,

(i) heat supplying means in said combustion section,

(j) catalytic vapor incinerator means disposed across said combustion section downstream of said heat supplying means, i

(k) a heat exchange section connecting with said combustion section, said heat exchange section having passageway means therein to receive and discharge oxidized exhaust gases from said combustion section,

(l) a fresh air inlet means connected to an additional passageway means in said heat exchange section to receive and to pass fresh air in indirect heat exchange relationship with the oxidized exhaust gases and a heated air outlet means connected to said heat exchanger to receive heated fresh air,

(m) a double ended heated air duct connected to said heated air outlet means at one end of said heated air duct and connected directly to said plenum section at the other end of said heated air duct thereby to pass only fresh heated air to said plenum section,

(n) regulatable damper control means across at least a portion of said heated air duct from said heat exchange section,

(o) a recirculating fan in said heated air duct,

(p) an adjustable cool air inlet means to said heated air duct upstream of said recirculating fan therein for introducing tempering air thereto,

(q) an exhaust gas outlet stack connecting to and extending from the downstream end of said heat exchange passageway means, and

(r) means for recirculating drying gases through said additional heat treating section of said chamber to continue the drying of the coated articles passing therethrough.

2. The coating oven of claim 1 further characterized in that interconnecting linkage means connects between said damper control means in said heated air duct and the adjustable air inlet means to said heated air duct for tempering air, a temperature sensitive means is positioned in sai-d heated air duct downstream of said recirculating fan, with said temperature sensitive means connecting to power operated control means which in turn connects with said interconnecting linkage means, whereby said regulatable damper means and said adjustable, air inlet means may be opened and closed responsive to changes in temperature noted by said temperature sensitive means.

3. A coating oven for heat treating articles to evaporate coating solvents and remove combustibles from the vaporized solvents, said oven comprising in combination:

(a) an elongated heat treating chamber, y

(b) means for conveying articles to be heat treated through said chamber from an entrance end to an exit end,

(c) a plenum section within said chamber and having openings in a wall thereof for directing heated gases over the articles passing through the chamber,

(d) a vapor combustion chamber having heat supply means and a catalytic vapor incinerator disposed therein,

(e) a vapor exhaust duct connecting said treating chamber with said combustion chamber,

(f) a circulating fan in said exhaust duct,

(g) a heat exchanger connected to said combustion chamber,

(h) means for passing air through said heat exchanger in indirect heat exchange relationship with hot gases from said combustion chamber,

(i) a double ended heated air duct connected to said heated air outlet means at one end of said heated air duct and connected directly to said plenum section at the other end of said heated air duct thereby to pass only fresh heated air to said plenum section,

(j) damper control means and a recirculating Vfan in said heated air duct, and

(k) adjustable cool air` inlet means to said heated air duct between said damper control means and said recirculating fan for introducing tempering air to the heated air duct.

(References on following page) 9 1G References Cited by the Examiner 2,804,694 9/57 Clipsham 34-86 2,938,714 5/60 Gerrish 34-86 UNITED STATES PATENTS 3,070,897 1/63 Lowe 34-150 6/43 Balley 34-150 ggg lgresct et a1. 345861555 5 PERCY L. PATRICK, Primary Examiner. 6/56 Hrldery 111111111111111- 34-86 NORMAN YUDKOFF: Examiner' 

3. A COATING OVEN FOR HEAT TREATING ARTICLES TO EVAPORATE COATING SOLVENTS AND REMOVE COMBUSTIBLES FROM THE VAPORIZED SOLVENTS, SAID OVEN COMPRISING IN COMBINATION: (A) AN ELONGATED HEAT TREATING CHAMBER, (B) MEANS FOR CONVEYING ARTICLES TO BE HEAT TREATED THROUGH SAID CHAMBER FROM AN ENTRANCE END TO AN EXIT END, (C) A PLENUM SECTION WITHIN SAID CHAMBER AND HAVING OPENINGS IN A WALL THEREOF FOR DIRECTING HEATED GASES OVER THE PARTICLES PASSING THROUGH THE CHAMBER, (D) A VAPOR COMBUSTION CHAMBER HAVING HEAT SUPPLY MEANS AND A CATALYTIC VAPOR INCINERATOR DISPOSED THEREIN, (E) A VAPOR EXHAUST DUCT CONNECTING SAID TREATING CHAMBER WITH SAID COMBUSTION CHAMBER, (F) A CIRCULATING FAN IN SAID EXHAUST DUCT, (G) A HEAT EXCHANGER CONNECTED TO SAID COMBUSTION CHAMBER, (H) MEANS FOR PASSING AIR THROUGH SAID HEAT EXCHANGER IN INDIRECT HEAT EXCHANGE RELATIONSHIP WITH HOT GASES FROM SAID COMBUSTION CHAMBER, (I) A DOUBLE ENDED HEATED AIR DUCT CONNECTED TO SAID HEATED AIR OUTLET MEANS AT ONE END OF SAID HEATED AIR DUCT AND CONNECTED DIRECTLY TO SAID PLENUM SECTION AT THE OTHER END OF SAID HEATED AIR DUCT THEREBY TO PASS ONLY FRESH HEATED AIR TO SAID PLENUM SECTION, (J) DAMPER CONTROL MEANS AND A RECIRCULATING FAN IN SAID HEATED AIR DUCT, AND (K) ADJUSTABLE COOL AIR INLET MEANS TO SAID HEATED AIR DUCT BETWEEN SAID DAMPER CONTROL MEANS AND SAID RECIRCULATING FAN FOR INTRODUCING TEMPERING AIR TO THE HEATED AIR DUCT. 